It depends on where you live, and what your local used bike market is like. And, how vintage do you want? Are you looking for something 10 years old or less, or are you OK with an old school 10 speed from the 70s or 80s? And what sort of bike repair skills do you have, so that if you get something a little rough, do you have the skills to do your own repairs, or will you be paying a bike shop for all your repair work?